arXiv subjects

Petr Honzík

Publications and source records attributed to Petr Honzík.

11 recordsLinked to original sources

arXiv2026

Boundedness of bilinear radial Fourier multipliers

We show that a bilinear radial Fourier multiplier operator with symbol $σ$ is $L^2(\R^n)\times L^2(\R^n) \to L^1(\R^n)$ bounded, $n\in \mathbb N,$ if the function $σ$ satisfies the smoothness condition $σ(2^j\cdot)Φ\in L^2_{1/2 +ε}(\mathbb R^{2n})$ for some $ε>0$ and every $j\in \mathbb Z,$ where $Φ$ is a smooth cutoff function adapted to the annulus $|x|\in [1/4,4]$. This condition is dimension free. We also apply similar reasoning to provide alternative proof of the initial result concerning multilinear Bochner-Riesz operator and prove an estimate for generalized bilinear Bochner-Riesz operator.

math.CA↗

arXiv2025

Bilinear singular integral operators with kernels in weighted spaces

We establish the full quasi-Banach range of $L^{p_1}(\mathbb R) \times L^{p_2}(\mathbb R) \rightarrow L^p(\mathbb R)$ bounds for one-dimensional bilinear singular integral operators with homogeneous kernels whose restriction $Ω$ to the unit sphere $\mathbb S^1$ is supported away from the degenerate line $θ_1=θ_2$, belongs to $L^q(\mathbb S^1)$ for some $q>1$ and has vanishing integral. In fact, a more general result is obtained by dropping the support condition on $Ω$ and requiring that $Ω\in L^q(\mathbb S^1,u^q)$, where $u(θ_1,θ_2)=|θ_1-θ_2|^{-1}$ for $(θ_1,θ_2)\in \mathbb S^1$. In addition, we provide counterexamples that show the failure of the $n$-dimensional version of the previous result when $n\geq 2$, as well as the failure of its $m$-linear variant in dimension one when $m\geq 3$. The relationship of these results to (un)boundedness properties of higher-dimensional multilinear Hilbert transforms is also discussed.

math.CA↗

arXiv2024

Reduction of Nonlinear Distortion in Condenser Microphones Using a Simple Post-Processing Technique

In this paper, we introduce a novel approach for effectively reducing nonlinear distortion in single back-plate condenser microphones, i.e., most MEMS microphones, studio recording condenser microphones, and laboratory measurement microphones. This simple post-processing technique can be easily integrated on an external hardware such as an analog circuit, microcontroller, audio codec, DSP unit, or within the ASIC chip in a case of MEMS microphones. It significantly reduces microphone distortion across its frequency and dynamic range. It relies on a single parameter, which can be derived from either the microphone's physical parameters or a straightforward measurement presented in this paper. An optimal estimate of this parameter achieves the best distortion reduction, whereas overestimating it never increases distortion beyond the original level. The technique was tested on a MEMS microphone. Our findings indicate that for harmonic excitation the proposed technique reduces the second harmonic by approximately 40 dB, leading to a significant reduction in the Total Harmonic Distortion (THD). The efficiency of the distortion reduction technique for more complex signals is demonstrated through two-tone and multitone experiments, where second-order intermodulation products are reduced by at least 20 dB.

eess.AS↗

arXiv2022

On pointwise a.e. convergence of multilinear operators

In this work we obtain the pointwise almost everywhere convergence for two families of multilinear operators: (a) truncated homogeneous singular integral operators associated with $L^q$ functions on the sphere and (b) lacunary multiplier operators of limited decay. The a.e. convergence is deduced from the $L^2\times\cdots\times L^2\to L^{2/m}$ boundedness of the associated maximal multilinear operators.

math.CA↗

arXiv2020

Initial $L^2\times\cdots\times L^2 $ bounds for multilinear operators

The $L^p$ boundedness theory of convolution operators is \linebreak based on an initial $L^2\to L^2$ estimate derived from the Fourier transform. The corresponding theory of multilinear operators lacks such a simple initial estimate in view of the unavailability of Plancherel's identity in this setting, and up to now it has not been clear what a natural initial estimate might be. In this work we achieve exactly this goal, i.e., obtain an initial $L^2\times\cdots\times L^2\to L^{2/m}$ estimate for general building blocks of $m$-linear multiplier operators. We apply this result to deduce analogous bounds for multilinear rough singular integrals, multipliers of Hörmander type, and multipliers whose derivatives satisfy qualitative estimates.

math.CA↗

arXiv2018

Maximal operators associated with bilinear multipliers of limited decay

Results analogous to those proved by Rubio de Francia are obtained for a class of maximal functions formed by dilations of bilinear multiplier operators of limited decay. We focus our attention to $L^2\times L^2\to L^1$ estimates. We discuss two applications: the boundedness of the bilinear maximal Bochner-Riesz operator and of the bilinear spherical maximal operator. For the latter we improve the known results by reducing the dimension restriction from $n\ge 8$ to $n\ge 4$.

math.CA↗

arXiv2017

Bilinear Spherical Maximal Function

We obtain boundedness for the bilinear spherical maximal function in a range of exponents that includes the Banach triangle and a range of $L^p$ with $p<1$. We also obtain counterexamples that are asymptotically optimal with our positive results on certain indices as the dimension tends to infinity.

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arXiv2016

The Hörmander multiplier theorem I: The Linear Case

We discuss $L^p(\mathbb R^n)$ boundedness for Fourier multiplier operators that satisfy the hypotheses of the Hörmander multiplier theorem in terms of an optimal condition that relates the distance $|\frac 1p-\frac12|$ to the smoothness $s$ of the associated multiplier measured in some Sobolev norm. We provide new counterexamples to justify the optimality of the condition $|\frac 1p-\frac12|<\frac sn$ and we discuss the endpoint case $|\frac 1p-\frac12|=\frac sn$.

math.CA↗

arXiv2016

The Hörmander multiplier theorem, II: The bilinear local $L^2$ case

We use wavelets of tensor product type to obtain the boundedness of bilinear multiplier operators on $\mathbb R^n\times \mathbb R^n$ associated with Hörmander multipliers on $\mathbb R^{2n}$ with minimal smoothness. We focus on the local $L^2$ case and we obtain boundedness under the minimal smoothness assumption of $n/2$ derivatives. We also provide counterexamples to obtain necessary conditions for all sets of indices.

math.CA↗

arXiv2015

Rough Bilinear Singular Integrals

We study the rough bilinear singular integral, introduced by Coifman and Meyer , $$ T_Ω(f,g)(x)=p.v. \! \int_{\mathbb R^{n}}\! \int_{\mathbb R^{n}}\! |(y,z)|^{-2n} Ω((y,z)/|(y,z)|)f(x-y)g(x-z) dydz, $$ when $Ω$ is a function in $L^q(\mathbb S^{2n-1})$ with vanishing integral and $2\le q\le \infty$. When $q=\infty$ we obtain boundedness for $T_Ω$ from $L^{p_1}(\mathbb R^n)\times L^{p_2}(\mathbb R^n)$ to $ L^p(\mathbb R^n) $ when $1<p_1, p_2<\infty$ and $1/p=1/p_1+1/p_2$. For $q=2$ we obtain that $T_Ω$ is bounded from $L^{2}(\mathbb R^n)\times L^{ 2}(\mathbb R^n)$ to $ L^1(\mathbb R^n) $. For $q$ between $2$ and infinity we obtain the analogous boundedness on a set of indices around the point $(1/2,1/2,1)$. To obtain our results we introduce a new bilinear technique based on tensor-type wavelet decompositions.

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arXiv2011

On the Good-$λ$ inequality for nonlinear potentials

This note concerns an extension of the good-$λ$ inequality for fractional integrals, due to B. Muckenhoupt and R. Wheeden. The classical result is refined in two aspects. Firstly, general nonlinear potentials are considered; and secondly, the constant in the inequality is proven to decay exponentially. As a consequence, the exponential integrability of the gradient of solutions to certain quasilinear elliptic equations is deduced. This in turn is a consequence of certain Morrey space embeddings which extend classical results for the Riesz potential. In addition, the good-$λ$ inequality proved here provides an elementary proof of the result of Jawerth, Perez and Welland regarding the positive cone in certain weighted Triebel-Lizorkin spaces.

math.CA↗